This invention relates to precision hydrodynamic bearings.
As part of the continuing advances in computer technology, greater and greater amounts of data are sought to be stored in smaller and smaller areal densities on magnetic disks. Magnetic disk drives typically include both a plurality of spinning magnetic disks suspended on a common precision spindle bearing assembly and also at least one magnetic read/write head which "flies" in close proximity to and at selected locations over an assigned one of the plurality of disks. The head reads or writes streams of data from or to "tracks" of magnetic interactions in the magnetic layer of a selected disk. The width of the tracks determines the number of tracks which can be defined on a given disk. The greater the number of tracks the greater the storage density. A magnetic disk drive assembly whose spindle bearing has low runout can accommodate higher track densities, and this results in increased storage density per disk.
Hydrodynamic spindle bearings are known in which the shaft part and the housing part have respective bearing surfaces which support relative rotary motion therebetween. By means of the bearing surfaces, one part rides on a film of liquid lubricant, e.g., oil, against the other part. These bearings generally have low runout, but require a continuously circulating lubrication supply. These bearings can be characterized by their means of lubrication, i.e., a lubrication system which is self-contained or which relies on an external supply.
Within the development of the self-contained lubrication type hydrodynamic spindle bearings comes the nettlesome problem of preventing lubricant leakage out of the bearing. In a magnetic disk drive, these losses can degrade bearing performance and thus cause read/write errors. As well, leakage of lubricant can lead to contamination of the magnetic disk surface, which can cause malfunction of the read/write process or even catastrophic failure of the flying head assembly.
In one known commercially successful product, the Phillips Video 2000 videocassette recorder, lubrication losses are minimized by using grease lubrication. The useful life of such bearings, of course, is limited by the stability of the grease. As well, rotational velocity is effected by the grease viscosity. No known disk drive spindle bearings utilize this technology.
Clearance type lubricant seals are required in disk drive applications to satisfy desired longevity. Clearance seal hydrodynamic spindle bearings, e.g., the ferromagnetic fluid type and the capillary seal type, are well known. However, they are strained by the centrifugal effects of the rotating part (especially a rotating housing), and are vulnerable to leakage of lubricant as may be initiated by trapped bubbles. Associated with the concern about trapped bubbles and lubricant blowout, use of o-ring static seals for assembly is often avoided, and then the lubricant filling requires a relatively elaborate vacuum impregnation procedure. Nevertheless, oil-lubricated bearings with clearance seals are of interest.
It is therefore an object of the present invention to provide a hydrodynamic spindle bearing of the clearance seal type which is self-lubricating and essentially leak-free by utilizing the centrifugal acceleration of rotation to keep the lubricant inside the housing. Risk of leakage through the clearance seals is minimal when the spindle is running due to the tendency of the centrifugal acceleration of rotation to keep the lubricant inside the housing.
It is another object of the present invention to provide a hydrodynamic spindle bearing of the clearance seal type which is not likely to suffer from seal blowout.